Modulation means and method



April 6, 1948. E. LABlN ETAL MODULATION MEANS AND METHOD Filed Aug. 24, 19'42 3 Sheets-Sheet 2 INVENTORS EM/LE LAB/N Da/ALD D. @fR/ ATT RNEY `April 6, 1948. E. LABIN E'rAl.

MODULATION MEANS AND METHOD Filed Aug. 24, 1942 s sheets-sheet s J l l l l y F I I I I I I I I I I I I I I 100, ooo pas. Pumas/sec.

6 Vl- Vl--JL-eqooo Ars/.55s.

H l *2D/W mi 4555/6 fNvEN-roRs EMILE AB/N Yoo/1A o o. @wss Patented Apr. 6, 1948 2,438,921 MoDULArIoN MEANS AND METHOD Emile Labin, New York, and Donald D; Grieg,

Forest Hills, N. Y., assignors to Federal Telephone and Radio Corporation, a corporation of Delaware Application August 24, 1942, Serial No. 455,899 16 Claims. (Cl. 179-1715) The present invention relates to pulse generation systems and more particularly to systems for generating time modulated pulses for use in communication systems and for other uses.

Several types of systems have been proposed for effecting communication by transmitting a number of pulses of current, the exact times of transmission of such pulses vbeing controlled in accordance with the speech or other intelligence to be transmitted. In some cases the pulses of current are themselves transmitted to a distance over wires, but in other cases they are used to modulate carriers so as to produce brief wave trains generally referred to as carrier pulses. Such systems vof communication have been described in U. S. Patents 2,266,401, 2,256,336, 2,265,

337, 2,262,838, and in copending U. S. applications 386,282 (now Patent No. 2,406,019, issued August 20, 1946) and 425,108, respectively filed on April 1, 1941, by E. Labin and on December 31, 1941, by E. M. Deloraine and E. Labin, as well as in a large number of other foreign patents and applications. In accordance with the systems heretofore proposed, the generation of time modulated pulses was eiected either by means of special vacuum tubes having cam-like target or masking means cut to a predetermined shape, or by providing multivibrator arrangements controlled by resistance/condenser time constants and capable of being influenced by the modulating signals so as to'vary the vibrator rate.

It is an object of the present invention to provide a simpler, more reliable, and more economical method of generating time modulated pulses.

More particularly, it is-an object to provide a system for generating time modulated pulses by the use of ordinary types of circuit components without requiring specially designed tubes.

`It is a further object to provide such a system for generating time modulated pulses which I shall be capable of being stabilized by a master source of fixed waves, such as a sine wave oscillator or a stable unmodulated relaxation oscillator.

More particularly, it is an object to provide such a system wherein the time of the generated pulses is controlled by a iixed unmodulated wave.

Other objects of the invention will readily appear to those skilled in the art from the following detailed description of the invention, taken together with the annexed drawings, in which;

Fig. 1 is a schematic diagram of a time modulation transmitter embodying one form of our invention;

Figs. 2 and 3 are sets` of `curves used for explaining the operation of Fig. l;

Fig.v 4 is a schematic representation of an arrangement for producing triangular waves which may be substituted for a portion ofthe system of Fig.1; ,qw 'Y I Fig. 5 is a' schematic representation of a clipping circuit which maybe substituted `for the clipping circuit shown in Fig.,1,; l

Fig. 6 is a schematic diagram cfa time modulation transmitter embodying aV modied form of our invention; f p

Fig. '7 is a set of curves used in explaining the operation of the system of Fig. 6;

Fig 8 is a schematic represenation of a modied type of clipping'circuit which may be substituted forthe clipping shown in Fig, 1 or that of Fig.6:

Fig. 9 is a schematic diagram of a modified form of system suitable'for producing pulses with a very small degree'of time modulation and particularly suitable for producing time modulated pulses to be received in accordance with the harmonic reception methods described in the abovementioned applications 386,282 and 425,108; and

Fig. 10 is a set of curves used in explaining the operation of the system of Fig. 9. l

Referring more particularly to Fig. l, I0 is a saw-tooth wave generator synchronized by a sine wave oscillator II and connected to deliver its saw-tooth output (preferably `via, a preliminary clipping amplifier I2) to the main clipping' circuit I3.

As shown in Fig. V1, this main clipping circuit I3 comprises a conventional pentode I4 connected in the usual` resistance-coupled fashion but preferably having a high resistance I5` in series with its control grid lead and having snorting-type jacks I6, Il and I8 connected respectively in the control grid return lead, the suppressor return lead, and the screen grid return lead. Except for this high resistor I5 and the jack I6, the circuit connections of the pentode I4 are essentially conventional, comprising onthe input side the usual input coupling condenser I9, and the usual grid bias resistor 29, the latter being connected through jack I6 to C battery 2|. The output side of the circuit comprises the usual load resistor 22 connected to the usual plate supply battery 23, as well as a conventional output coupling condenser 24. The" screen is biased positively by screen battery 25 in the usual manner.

1n addition to the inpuoappuedfrom saw-tooth generator I0 via amplifier I2, an additional lower frequency modulating signal is applied tothe circuit I3 through the jack I6. As illustrated in Fig. 1, the modulating: input consists of speech from a telephone transmitter 3l! which is applied via. amplifier 3I,V transformer 32, and plug 33 to jack I6 of the Vmain clipping circuit I3, `being thus applied to the controlgrid' of pentode I4` in series with battery 34.

The output fromthe main clipping circuit I3 is fed through` a wave1differentiation network 35 which may be of any -Alnown ,typeand then through another similar" `diiferentiat,ion, network 36, which may alsonsupply amplification-ii` desired. 'Ine-outputfrom circuit'fss yis thengappled to modulate a radio frequency amplifier 38 which is excited from a suitable radio frequency source 3l so as to produce a train of carrier Waves responsive to each modulating vimpulse received from the circuit 36. The output of amplierv38- is then applied to antennaf39 for-radiationtoa distant point.

The operation can best be understood by consideration of the curves of Figs. 2 and 3 in connection with the circuit of Fig. l1.v "The-isawf-tooth generator l produces waves such as-shownlinvj curve U of Fig. 3. The preliminary clipping amvoltage flbatteryrisljust equal tothe peak voltage of the' loudests'peech' wave's arriving over transformer 32. Thus the tip Iof 'plug' 33 is positive4 ,with v`respect to the i sleeve thereof "at 'all times vexcepting en the extreme negative peaks of the speech waves. v4'For convenience, it may be V- further assumdthat vthe potential of bat-V tery 2 l s is -polarizdtobias' the control 'grid positively .insteadormgatively and is sufficiently great that whemthis voltage is superpose'dupon the voltage -of lcurve/,the most negative portion of the curveVextends `only slightly below cut-off. 4Ifthis be..so,-and'i'f'it be assumed'that at the-moment ug-nder consideration, the speech signal`arri'vinglfrom` transformer 32 has' its maximum negative valejthen'the resulting wave applied rto the-control v.grid .of pentode I4 will vbe positioned as shown in curve W of Fig. 2'with its most 4negative portionv only slightly below the cutoff -thre'shldEco. 'I'f-theth'reshold of "grid currentEgctis:'faiilyclosev to'tlie 'cutoff threshold Mathe-greater part-.ofthe voltage wave'will lie above boththesethre'sholds as shown in curve W m-Figiz.- Y j Consideringnow in. greater .detail the action ofj-the pentode inresponsetothe applied wave Wshown in .Fig. `2,"it.will '.be seen thatwhen this Wave starts :upward from 'its lowestvalue below lEcp there iswat `iirstnoresponse`untilthe 'Wave passes-above the threshold, Eco. vThen as jthe Wave continues'to riselfrom'Ece towardfEgc'an ampliiied` voltageywave.is-produced in the "output circuit' of .the fpentode, rtheA form of this" voltage wave being shown-in VcurveX'of `F1g.^2. (Actually this` outputvoltage wave is-f opposite sign' from fthe curve W, as indicated by the designations uf- 0-| at the right of curve Z. Also, these threefcurves-have their zero line oiset with respect to the-zero line of curve W to further fay cilitate cmparisonJof curves W and X. In adfditionfit lwill beneted that the curves are drawn as if no -fampligcat'ion occurred in any of the stages Nalthough it is clear that amplification will :inherently occur in the clipper stage and maybe included in other stages.

The output wave X 'is next differentiated in network 35 to yield a series of alternately positive andnegativev pulses -asshown injcurve 'Y-.of Fig. `2. ,"The upward '(i.e.,negative), pulses corT responding to the .inclined Aleading edges'of the nearly square-'waves have 'a duration {theoretically corresponding to the "durationl of` these inclined rising edges ofthe wave' X, "Wl1ijle the downwardpulses produced by the vertical trailing edges :of :the nearly 'square "waves X have` theoretically "greater-amplitude but zero duration.

The' alternate positive and negative pulsesfrom the "rst differentiation network35 `are then transmitted through'the second similar network 35, a suitable amount of ampliiica'tionjbeing preferably included in Aone or both of these networks. The .-eiectofithe second 'diiere'ntiationis' toproduce an upward pulseof`eXtremenarroWness`for each'verticalrise of current in kcurve MAY and to produce -ajdownward pulse' of similar narrowness for each vertical fallingportion of :curve Y. Thus, each of themoderately narrow upward-pulses of curve Y would be converted intoa "pair of' pulses substantiallyjoffset. with 'respect to `one another, the "lrst of 'these Abeing'an upward pulse, 'the second'bein'g -a, downward pulse, buteach of'the very narrow downward, pulses of curveV Y is k"converted intotwo pulses which aresoV nearly simultaneous that their oisetting is` not readily apparent. kAll these pulses are clearly shownin curve Z of Fig. 2. A Y The'output of the second diierentiation-network 36 is then applied to modulate thee radio frequency amplierBS, thus producing-brief wave trainsjwhich-are radiatedA from antenna- 39. The

modulated' ampliiier 38 I is soarranged that 4riormally no carrieris radiatedtherefrom and only positive vmodulation signals "are. effective to .cause it todelfiv'er"carrier'poweito-itheantenna. .Therel fore, only the* down-ward i or Ipositive pulses Itof the input wavelbut'to "facilitate-.comparison 'of the curves it-is-'slflown-.asif there wereno re'- Versalof signi) fWhenthe inputvoltage Wave lW passes above the `Vupper threshold. of Een; the

output voltage of thepe'ntode .abruptly ceasesto vary, a since` the commencement f L grid current iiow.l imposesfsuch a. highl load fas toeverloadthe driving .stagean'dthe couplingV condenser I9.' In addition,..theiflowrgridcurrentthroughresistance l5 -lgives riSeto lajvltagedrop across thisresistance which. subtracts 4.from 'the grid driving voltage thus further a'fectingthe'lniiting action.

'Ihe .output'vltage wave from "the pentode lll-will therefore correspon'd exactly tothose portionsgof curvewwhich lief between "E coand AEgt as can'be plainly seen by "comparing lcurves 'W I curvev Z are effective, the upward` lones :"beingj. in effect crit-olii byfthe iinhere'nt response vcharacteristics of'theamplilier. f l

It should belnoted thattheeiective :downward pulses of curve 'Zfcorrespond Lto ltheiidownwardly concave corners pq, 1', etc., of curve X, .while the' upward pulsesfo'f curvel Z correspond'. to the upwardly vfconcave corners '.r, Jy, La, ietc., of z this curve. f I'Ihus,v`thelt irning^of1the effective!orrd'ownward-.pulses 'of curve `Z dependsLuponthetime of intersection ofthe inputwave "Wfwiththe upper threshold'Egc. l' It should'L-be funderstood, howeverfthat if desired,-Y oneI orthe! other ifofthe diierentiationi networks 35 Jand I3 62 may .bei cnnected to 4effect `a phasereversal; i lin which fcase the pulses effective in modulating the 'fcarrier would be those derivedvfromilcorners: az, y, of curve X and which depend :"for their ttiming upon v`the moments 'of 'intersection `of curve l W with th'elowerthresholdiEco. i r

The above descriptionfofoqcieration, vas `well: as the associated curves W, X, Y, Z of Fig. 21re1ate thereof asmay be desired.`

S to the operation during the intervalsV when the speech wave or other modulating signal has substantially its maximum negative value (so that the potential of the speech Wave just offsets the potential of battery 34, giving the tip of plug 33 a zero potential with respect to its sleeve). In contrast to the conditions occurring during such time it will be useful to consider the conditions occurring during the opposite extreme of the modulating signal (i. e., when the tip of plug 33 has its maximum positive potential with respect to the sleeve thereof). p Operation during the latter condition is illustrated in curves W', X', Y', Z in the lower part of Fig. 2, these curves being aligned with the corresponding curves W, X, Y, Z for ease in comparison. The operation of generator I and preliminar clipping amplifier I2 is unchanged regardless of the potential of the modulating signal, and consequently the curves U and V apply just as before. Because of the ,positive potential of the plug tip `with respect to its sleeve the control grid of pentode I4 is biased much less positively than before and therefore the applied blanked sawtooth waves W are positioned lower with respect to the cutoff level Eco. In the case chosen for `illustration it is assumed that the speech signal come the positive bias of battery 2I and `thus tov bring the mean control grid potential below zero. Accordingly, curve W' is illustrated as lying predominantly below the threshold Een. Actually, it is usually preferable to employ a smaller modulating signal so that the grid bias would become a little less positive andthe curve W' would be positioned only a little lower than curve W.

The clipping action of the circuit I3 takes place essentially as before thus producing the wave X' in the same manner previously described for the wave X. Because of the different positioning of the curve W with respect to the two thresholds Eco and Eea, however, the generally rectangular prominences of wave X' are somewhat narrower than the corresponding ones of wave'X. The differentiating network 35 produces curve Y' withV alternate upward and downward impulses in the same manner as described for curve Y,` but owing to the narrower prominences of curve X', the time interval between each upward impulse and the succeeding one is substantially smaller than for the curve Y. The second differentiation in network 33 converts each pulse of curve Y into a pair of offset pulses of opposite polarity a pair ofmore'or less perceptibly offset pulses of opposite polarity, the curve Z being thus similar to curve Z except that two successive offset pulse pairsare spaced somewhat closer together.

The pulses from curve Z are applied to modulate amplifier 38 and as previously described only the downward pulses are effective for this purpose. The short wave tra-ins of carrier frequency radiating from antenna 39 therefore have their timing dependent only on the moments `of intersection of curve W' of the upper theshold Egc.

If it is desired to use the pulses for some other purpose than to modulate amplifier 38 (e. g., for direct transmission over the wire) a clipping or half wave rectifier circuit may be employed to select only `the downward pulses of curve Z and Z' or only the upper pulses In the above described embodiment of the inventionl the pulses produced are time modulated in such fashion that each pair of useful (i. e., downward) pulses has one pulse fixed and one pulse which moves in time in accordance with the modulating signal. For many purposes it is desirable that the two pulses should both move in symmetric fashion, one being advanced by the same amount that the other isretarded.

Inl order to achieve this result the wave form `applied to the preliminary clipping amplifier I2 a multivibrator synchronized thereby for produc- 4I is applied to an integrating network 42 thusV 'producing zigzag waves of symmetric triangular form. The wave generating arrangement of Fig. 4 may be substituted for elements I0 and II in Fig. 1, and in such case the output waves which would be obtained from the second differentiating circuit 36 would have essentially the saine form asshown in curves Z andZ except that two successive downward pulses would shift equally in opposite directions in response to variations ofthe modulating signal.

Instead of plugging the plug 33 into jack I6 as shown,*this plug may be inserted either inthe jack I1 or I8. When inserted into either jack II or I8 only the cutoff threshold but not the grid current threshold will be influenced by the speech signals (assuming that the sawtoot'h forni of Figs. 2 and 3 is employed). Therefore, the corners y, a of curve X will not vary with the speech wave and theV spacing of these lower corners will be the same for X as for X'. The height of the trapezoidal waves X and XA will vary in accordance with the speech signals and the spacing between the upper corners will vary correspondingly. Thus, the corners p, qi r of curve X will differ from the corresponding corners of curve X' even through the lower corners of both these curves have the same spacing. Only the downward pulses of curve Z and Z' therefore will be useful in` such systems for use as time modulated impulses.

Fig. 5 represents another form of clipping circuit which may be substituted for the clipping circuit I3 of Fig. 1. Instead of employing the two grid thresholds of one single tube for eiecting the upper and lower clipping actions, the arrangement of Fig. 5 employs only the cut-:off thresholds of two different tubes. Referring more particularly to this igure, the main clipping circuit designated generally as I3 comprises two pentodes I4' and I4 connected in a conventional two-stage resistance coupled circuit, but having three jacks I6', I1' and I6" included in the control grid and suppressor grid return leads of the first pentode and in the control grid lead of the second pentode respectively. The elements I5', I9', 20', 2|', 22', 23", 24", 25 correspond exactly to the similarly numbered elements of previously described clipping circuit I3 while the elements 23, ZI", 22", 23", 24" `and 25" are corresponding circuit components for the second pentode I4". Since the grid current threshold Egc is not intended to be used in connection with this i'7 .may:be-madesonconventionall vail-ue even .if:.this .makesithez-rgrid bias comparatively larger-kin se- ;lectingathe: ibiases-,lpri-me consideration shoulda-be .lowsz The. input-Waves.applied-,tothe pent-ode I4 sweep. from belowr towabove :.theccutolgrpointf,and .thus produce ar-responseinwhieh is atgirstzerofa-nd thenisuddenlyrrises. 1fWhetherforvnetfthese'waves later zpass; a comparatively rem-cte; grid :feux-rent .threshold Iis immaterial. :The output. rwaves 1 which i are, sof course, of reversed :.polarity, are

.then applied tonthesi second pentoded 4 through vthe output tcoupli'ng .fcondenserf 24'; :and there '.:thesewaves are; Yclipped :by 4the cutcfff.-threshold .ofthe second` tube el 4'. :Because of: theinverted :polarity of thexiwaves this; secondi`clipping--,(.al-

;though.vitr removes; the negativemortions ofwthe waves and .passes only thepositive-iportions) 1W-ill have the `electA of .cuttingioiuthe ttipspsineesthe rtips ofpthe Waveslzare fnovvffnegative. "JIT-huSf'the wtwo: successive clippings', each- .of which-.cut ioi the negative `.portions offthefwaveaearel equivalent to the double or-.gatef clippingflaction;previously :described for 'circuit I 3. The -biases e2 I Yand@ I can readily .beadjusted tofhrlng. theeiective v clipping levels ofthef. two tubes aslclose together :as-.may loe desired. Thisis one advantage .roffthis type of circuit.

If. the plug. 33l is plugged' to jack-.I-Iitthe .eiect 4will be to l displace :'iboth. thresholds :withsrespect tothe input wave or more-accurately to displace 'the' input Wave with respect: to .bothvrst threshaolds). Such faction. istherefore.iexactlmsimilar tof the actioni of Y.circuit-:I3when ythe plug $7331.15 plugged into jack lI 6 thereol, Ifffhowevenwthe :plug:isinsertedwinjack I'I' orpjackfIBWof) circuit I.3; the modulating faction: isrdifferent. Medalla- .tion applied tjack I 'l .variesonly sthef-cutaoff ,level of tube:v I4" while mod-ulationg-appliedrtoutube f. It"V varies: only .the enti-'offs' levelxoff-.tube .f M.

:.Each; of these types zgof.modulationv iztherefore, moves `only one thresholdofzfthedouble yclipicring circuit and care should be talrenfthattheputput l pulse chosen^for utilization hassitsltime determinedp-by the threshold which is th-ussmoved.

vlInstead `ofzernploying .fsawtooth 'or triangular Waves as -the'basis `for derivation of theA time modulated :pulses itA is, possible -to employ rsimple sine waves. Theuse of fsuchasine fwavesfresmts in Vaxsimple structureandtendsto produoemore f er. I ID and preliminary clipping amphi-lenV I'L2lto *8 .Eor ythe `sake `of -,f .feneralityfhowever, II3\ is illustratedflas: .beingof .adifferent y. type 'femployingf `dry recti-iers instead ...of vpentodes. The-two dry rectiers -IILand Il5-varecon 'nectedf back- Eto Y :back and a Tsmall l. `positives-volt- -age isi-applied f-from. battery Y IIS through. .rel-sistor. |20- to the 1-intermediate` point between themv :The-resistor |20 ispreferably at least'sev- .eralatimes larger .than-fthe low forward resistance -lofvthe rectiiers,- although it-shouldbefloWl-fin comparison with the thigh fback resistance thereof. :The input -wavez .fromwamplien I I 2.is applied through f coupling= Ycondenser I2 I to f resistor. 122 .which .is preferablyseveraltimes vlower than resistor 1:20. The outputwof fthecircuit. is delivered across another resistor- I23 whichnmay `.he ofthe same order `of -mag'nitudeas resistor; I-22. .It 7Wil-lbe understood Ithat if'thel followingstage has a. ,suitablevalue of input.- resistance, resistor .lIZS'l-may be omitted.

1Forf.modulating.theclipping action, Ispeed .sig- '-.nalsr fnom telephone transmittery I 3|J-rare supplied .over thespeech amplier I 3| and transmitter. |732 via -the plugsl 33 torjackl I6. `TheI'battery-JI 315. is in seriestherewith and forconvenience inL descripition'this-battery maybe assumed .tohave justsufiicientfpotential sothat at .the maximum ,negative speaks of the` speech v-Wave the tipzand sleeve of ...theplug I331have -the same potential; thetip-be- .l-ingpositive at' all-other times.

, Theaoutput of main .clipping .circuit .I I3 is-ed to the output' portionofthe yequipment ,compris- -ingfelementsIS436, I3'I,II38 and. ISS-Which .correspondto the similar numbered 4'elements of 1. f The-operationelf the system-fshown-,nfig V6 `can best beunderstood Vby' consideration oft-.this .figurer in conjunction vwith the curves-of Fig.l '7, ,since `wai/ies .from :source I I I pass -through .am- .plier-... I-I`0` and .preliminary ..clipping.farnpliiier.- I I2 .andl are .thus converted .into the approximately ..trapezoidal.form shown in curves A and'A. oflig. (.7. ...InthecurvesofLFig. '7 -it` isaSSume'dZthatjjl-,he upper vand.lovveroluarterLof thejsine wave ilhave Hbeen..remove`d '.by '.the Aclipping amplifier I YI2..so that :only-fthe .central .halfmemains 'Since .it is not, essential .that the clipping `action of.' ampli- `,lerI I,2'Jbe a'sharpelipping action giningjperfect- ',ly.,square .corners .the curves IA. andJA iFig. '.7 `havellbeenshovvn with slightly .rounded corners. 'The ...curve A. represents conditions when? the .speechiinput .wavehas its maximum YVnegative value .so that -the .total .voltage vproduced -by. V.the .speech.Waveland,.batterytogether; is Zero. Atl this .timelthe .main .clippingcircuit acts,A just .as if "the plugvl33 .werenot .plugged in. l'I'hev inputv WaVeIA `is` symmetrical with-re,spect..to the .zero line as :shown so -that.' thepotential atthe oleftfhand. side of the rectifier ll'd variesrequallyabove.andbelow .ground :.potential. .Because eithewrectifyiingaaction.of..elementr II4.the intermediate point FM.: of the clippingacircuit. .is .unablelto' be .raised abovefits natural' ,orv open .circuit potential .since it` cannot .receive current through Y.rectiiler L ;,I.I 4. :Thus,-the potential of, pointAM willliolloyvthe'l in- ;putpotential .onlyupto lthepoint whenthe `input potential equals the potential of battery I I9. Any l.potential riseilbeyonfd.thislimit (represented in ,1.Fig.\7-.1bya dotted line .marked fupper ,clipping .limitf .WilLnot be-.transmitte`d .toepintMso .thatr only .those portions .of curve A lying' i below suchv upper -clipping limit will pass l. through vto ...point M.. .In transmission from..point"Mlto' the output of the main clipping circuitlthe rectify- ,..in ,-.75 ingestion .of element] I,5;similarly.eliminates all potential variations below ground potential, since the point M cannot draw current from the righthand side of the circuit but can only deliver current thereto. As a resultall portions of the curve below the lower ,clipping limit (i. e., below the Zero line) will be blocked and not transmitted to resistor |23. 1 l

Therefore, theonly parts of curve A whichl will be transmitted to resistor |23 will be those portions between the twodotted lines marked, respectively, upper clipping limit. andlower clip-ping limit of Fig. 7. Theresulting truncated vtrapezoidal waves are shown in curve B of Fig. 7.i (Actually the corners of such waves will notbe perfectly square, but since -it is desirable to have the clipping as sharp `as practicable the corners are shown in the idealsquare form.)

As in the previously described system, the clipped waves are next transmitted throughthe two differentiation networks |35 and |36which produce an output proportionate to the second derivation of curve B. The `output of the second derivative circuit |36 is shown in curvelC.

The above description of the curvesA, B `and C relate to the action of the main clipping cir- 10 bias to `rectiiier` SI5 while the upper half of the split secondary of transformer 8|6 is positively biased by means of battery 8 I8 connected through secondary of a speech input transformer 6|9. A jack 820 enables application of speech to the primary oi'transformer 8|9. Preferably, by condenser 82| connected across the secondary of .transformer 8|6, it is more or less tuned to the 10 kilocycle frequency thus minimizing wave distortion and increasing amplitude. An output resistor 322 `and an output coupling condenser 823 serve to couple the full wave output of the cir-l cuit with the succeeding stage.

The operation of this circuit is analyzed inconsiderable detail in our copending application, Se-

rialNo. 455,897, led on even date herewith'for Push-,pull modulation systems, now Patent No.

, "2,416,329, issued February 25, 1947. Briey,t`ne

fcuit ||'3 and the differentiation* networks` |35,

|36 during a maximum negative speech Wave peak. Corresponding Voperations during aimaximum positive speech -wave peak are illustrated in curves A', B' andv C and can readilykbe understood by comparison with curves A, B and C. During the positivespeech wavepeaks when the tip of plug |33 is positive with respect to the sleeve thereof, la negative Ibias is thereby applied through low resistor .|22 tothe .leftsideof rectifier H4 and thus the truncated sinusoidalinput from amplifier |2 is superposedonthis negative bias so as the resulting .wave A lies principally below zero potential, as shown in the lower portion of Fig. 7. Accordingly, the trapezoidal wave form B produced bythe clipping action is correspondingly narrow; andthe corresponding pairs of pulses of C are more unequally spaced.`

The output from network |36, Whether it has the form of curve C or :curve C' 0r some intermediate form is then applied to amplier |38 to modulate the latter. Only the ydownward pulses of curve C which represent positive polarity voltages will be effective tocause the radiation oi carrier although, ifdesired; a phase `reversal may be incorporated in one of the.`differentiation circuits to render'only theother pulses effective. i

If the plug y|33 is inserted into jackA or jack i8, then instead of displacing both thresholds together with respect to the wave, the modu-` lating signal applied to jack I7 l1 willdisplaceithe upper and lower clipping .limits in opposite directions while if applied to` jack H8 it will displace only the lower clipping limit.. Care should therefore be taken that'the pulses of curveslC and C which are chosen for utilizationsnould be dependent upon the clipping limit which is moved. i

Still another form of clipping circuit is'shown in Fig. 8. Referring` more .particularly .to this figure 6M and' 8|5 area pair of recti'ers ccnnected .tothe split secondary of transformer VBlii so as to fully rectify any vWaves applied to this transformer. The split secondary of transformer iihas its two halves joined by a condenser i'i Whose impedance is preferably `moderately low for the 10 kilocycle foundation Wave while being substantial for the speechfrequencies used for modulation. The lowerihalf of `Vthis split secondary is directly grounded so-as ,'GQ apply a zero circuit serves to full Wave rectify the 10 kilocycle sine applied thereto. During intervals when the speech arriving over transformer 8|9 just neutralizes the voltage of battery 8|8 the, circuit acts as a perfectly paired full wave rectifier giving a series of half sine Waves which meet at sharp cusps evenly spaced a half cycle apart. The op* posite extreme speech voltage when the upper rectiiier v3M is strictly positively'biased, the rectifier is unbalanced and. the full wave rectified output consists of a series of peaks of alternately large and small amplitude meeting each other Y in sharp cusps Whose time spacing is alternately longer and shorter than half period.

It will be clear that when outputs `containing such cusps are applied `to the two diierentiating networks and |36 the outputfrom the network |36 Willhave'large voltage pulses corresponding lto each sharp cusp and will have at all other times substantially small voltages since it is Well known that'the second derivative of a curve is proportional to the sharpness of the curve at any point thereof.` In case triangular waves such as those of Fig. 4 are used as the input in the system ofFig. 1 while the clipping circuit of Fig. 8 is used in place of |3 thereof,` it may thenV occur that the similarity of curvature 'at the peaks of these triangular waves to the cusps lproduced by rectiiication will be of the same magnitude. In spite `of Ysuchsmilarity of magnitudes, however, the pulses corresponding to the peaks can be readily distinguished from its corresponding cusps -sincethey will .be of opposite polarity. Y

Although clipping circuit ||3 `has been shown in connection with the system in Fig. 6, it will be understood that any one of the three clipping circuits i3, I3( or l| I3 may be used in either the system of Fig. 6 or that of Fig. 1 (or in the system of Fig. 1 as modified by replacing `Ill and With the circuit of l'lig.Y 4). It shoulld also be understood that each of these circuitslmay be further replaced by its equivalents, for example, by substituting electronic diode rectiiiers for the dry rectiiiers ||4 and ||5 in circuit 3, or by substituting triodes forthe pentodes in circuits |3 and |.3. In fact, the system at present believed preferable corresponds to Fig. 6 with electronic diodes substituted for the d ry rectifiers illustrated. f

It should also be understood that only one threshold is essential in circuits |3, I3 and ||3,

explaineds to #block--fthe-- transmission of l lcer-tain ones of the pulses. For controlling'thissblocking action-a portion ofjthe 50 vkc. f sine Waveenergy from-- source 9 l I is ledofi ftl-nfough` vvphase.' shifter ,set otpuises from. the subsequent, differentiation circuits is to be utilized. Injljiig;howeyenyhoth rectiersplay a useful. part.

.- Although 4displacementl.of 'the oriticalthreshxlmayfleeef anysuitalole-type capableef operating Vata--subharmenie of twice-'the frequencyof asyncroniAzlng `input. The` tmulti-vibrator 94 2 should type adjustedytol-operateat 20 `ke.,-loein. g synchrotermine. .the timing/of ,the ,pulses;.l.lliimately Lob@ .used) .with respect. to. .thevfoundation `-Wayesds preferably effected :by V,applying theunodulating signal .to vone.of-thefjacks ll, H1 or. I l8 ofFig.

. applied -over phasefshifter :94 I `Gif necessary a full Wave rectiienmay'beiinterposedbetween the 1- sourceand --theanultivibrator' to facilitate. synfohronization in this .manner) This .multiviical threshold :with respect .to 1 ,the foundation .wa-ves may be achieved by plugging ,into jack .109. When themodulating.signal-is. appliedyto jack VI 09 so as ,to modulate the. amplitude. .of the foundation `Waves the time displacementoftpulses25 -may befeiected in: one of two yWays depending aon-fthe initial fd-isplaeement of thecritical thresh- I'0161s with `respect -tothe .center line fof. the .foun- :fdation awave- ,;I;f, for =..eXamp1e, the critieal Y .thresholds 1 are placed symmetrically i abo-ve and "'30 below the center dine f of the ftoundation.waye,

r-yariation of :the amplitude -pithevfoundation :Wave will :produce at .-thefoutput -of Y,the clipping circuits a rectangular .WareV ef constant :width lhut ewith sideswwhosegslones lv ary@with the amplitude modulation. Douhle;.diierentiation@et` this-,wave 1 will .produce time @modulated :pulses 3 similar ,ato f the pulses describedpreyiously On the .other handcif the.critiealethreshoid; is` offsetzwith respecttoythe; center -l-ine, it iselear `-thatthe .absolutex number. .of...vo1ts:.0fY ;-o1;set;ting onthe critical.thresholdwith-respect, to the-,eenterl `line fof the foundation :Waveiwill'remain constant and' -thereforeas .tha-:foundation -mayejdou- "bles in-fam'plitude: .the threshold which vutaswinitially oiset half-.Waytbetween 'the center. line .and =thef xedline Will only. Ibe. offset -one-.quarteraof -thexyay from thecenter line to the peaks. '-"Ihus,

'-ifrv thepositionl'of the threshold isf-measured mot.. 50;

1in terms of absolute ll-voltsdoutiin:,terrns-ofzfthe foundation wave which it intersectsvsiitiis iclear v^ that" theamplitude modulation .ot :thezfoundation "Wave ^Will,-in thepresence -offa substantial-initial Joffset; produce-a substantial -var-iation 'ini the rirel- ,155`

ativegposition -of thesfcritical threshold-withstaspect to thefoun'dation Wave.

Q represents a-modied timecmodulation `systemwyhich is arranged -to generate-Mftimes f off al1-butithedesired-ones thereof. *Theactual pulse..producing element of-thesystem-of Fig.

69 may be Voi any=desiredtype. "For-convenience Yand '|36 fromFig. 6. The speech source- 4930 which. supplies the modulating signals; topulse `Vproducer 900 imay be assumed -tofiineludeeele- Hasmany pulses asare--required and then to-block 60.=

'.".kc.wav.es to vthe 4time modulated jpulse producer .70 :1,1900 which may,'for comen-ience, I beassumed to comprise elementary circuits-|1105 H2, l^i3, |y35 portions;'of-y its generally square .wave Youtlziut .are -of considerably shorter duration-than the-negative portionsdthereoi,` the output-from such-.mul- *tivibratorfbeing :then generallyoi the' .form shown kin cur-Ve' G off-Figs 1 0'. 1 The -output ifrom the ,multivibrator-942 is applied to control the lbloeking of r circuit 1940,t thus determining which. .oi-the pulses fromA cireuit 00-will`be `blocked. andwhich V4willbepassed. -The output'.=irom .the circuit is-app1f'ed. to-.any-=.suitable s utilizatio'n r-iquipment x950. Preferably,=-1this equipment .850 ,comprises -elementscorresponding'-.toli`s'l, L38; 43.9 of:.lig.1.6. i The-operationof the i system of :FiggS can .best ^leefunderstood in. conjunction. with:4 the .curves of resented hy-.c11=1w'e':*EA andf .serve .to actuate the -gpulse-produceril in rthe same Way. as :described zineonnection Withfig. 6.

was explained -in-.connection with 'Eigl 6,':the tima-positioneff .the .upper ,(orfpositive). `ones of lthe-pulsesedelivered :(.fro'm' .136) l:dep.en ds.u1: on the -level-ofthe. upper-'clipping- `lirnit-,ivtitlfi respect .to the foundatiorhwave, Kbeing: thus determined: .by

z .theipotentialoff battery H9 andjack Ici'l (,see'Fig.

,upon the .foundation'waye v.through.svi/itch [A l and cja'ok M6 ((seeifigfi) The .dottedline @extending across. representsgsohematiully the .relative positionh of etheieffectiyefupper threshold .',Withuespeetttocthe foundation .'Wle. @The lippe? pulsesao curve vulL. there-fore, corresponde .to fthe intersections..oig` this-dine. e,- with;the *..curye '-:In' ordento rendenineffeotive. all hutcertainones of fthe .pulses .of. curve F, the output Wave -G from .themultivibrator.:V 9.42 is-applied tofcontrol; the :y -.blockingeircuit i940. Duringuthe brief positive .intervalspf cuz-ye. G, .theircuitrd is .unblocked LAso ythat any .input applied thereto can pass Lthrough .to utilization.emi-ipInent511. l3nt-irreY all 4the rest .-of .the .time the .blocking-cincuitz 940 is .blockediso asto beincap'able .oi-transmitting, any `iwaye formappliedlto its..input. Accordingly, of all of the pulses from curve F, only those shownfin 1 curved-Icareftransmi-ttedftoithe utilization .equiptheiutilizationequipment responds only to the -upum-.dly--fdirectedpulses .ofV `curare; the i down- Wardly7 directed. tpulses 'thereof' being. effectively @blocked-bytheinherentaotion of the utilization equipment. :It will-be understood; however, .th-at the-.wavesamayube.reyersedi so,l aste.. employ the other. pulses `if this. is preferred.

`.75-01 theupper-pulses ofcurVe-:Fis transmitted, .In

vment. tAs-in-the. ease.o11ig. .6,.it.is assumed that u 13 view, however, of thefactthat the sine wave source 9H is at 5 times the frequency shown for use in the system of Fig. 6, the total number of upward pulses according to curve H will be the same as in the output of the system of Fig. 6. The amount of deviation of any one pulse from its mean position will be less for a given modulated signal voltage, since a given displacement of threshold e with respect to curve E will produce only one fifth as much `time displacement at the intersection points as will be produced by -the same displacement of a corresponding threshold across the sine wave of one fifth the frequency.

It will be understood that the factor of multiplication may be any desired num-ber although preferably an odd number is employed. Thus, nstead of one could take 3, 7, 9, 11, 13, etc., as factor. 1f the factor be generally designed as M, the sine wave source 9i I should have a frequency the factor M being, therefore, 5. The resultant curve F, contained 100,000 upward pulses per second and 100,000 downward pulses per second. By means of the curve G which passed every fth one of the upward pulses (as well as everir fth one of the downward pulses), the number of upward pulses was reduced from 100,000 per second to 20,000 per second, i. e., the desired number. The downward pulses of Fig, 10 could-have' been suppressed before transmission through circuit 940, but in the case chosen for illustration, it was assumed that this was unnecessary since it was assumed that the utilization equipment would respond only to `the upward pulses of curve I-I. y

Although for convenience, the system of Fig. 9 has been described upon the assumption that the equipment 900 comprised pulse producing porti-ons from Fig. 6, it will be clear that such apparatus 900 might equally well incorporate the corresponding portions of Fig. 1 Similarly, also, the mo'died systems obtained by substituting in Fig. lor Fig. 6 any one of the clipping circuits I3, i3', II3 or the -circuit of Fig.l 8 might be used for the pulse producer 900. y

The system of Fig. 9 is further applicable to other types of systems described in our copending application, filed by us of even date for Mdulation system. Such system is very similar to that of Fig. 1 or 6 of the present invention except that elements such as 36 or |36 of the present application are replaced by full wave rectifier and limiter equipment thus eliminatingthe second diiferentiationstep described in the present application. At the same time that this is done, the upper and lower clipping limits of the clipping circuits employed are brought Vas close together as conveniently possible so that the interval of time required for the passage 'of theV within the scope and spirit foundation wave from the lower to the upper limit is only a small fraction of' a cycle. By such an arrangement the pulses produced by a single differentiation are rendered sufficiently narrow and are used after full wave rectification for application to the desired utilization circuit. In incorporating such asystem inthe system of Fig. 9, all parts of the system between the master oscillator and the utilization circuit (i. e.. the narrow two-level clipping circuit followedby a single differentiation network and then by al rectifying limiting network and preceded bythe required ampliers and preferably by preliminary clipping amplifier) would 4,be incorporated in the time modulation arrangement 9.60 ofFig. 9.

Another type of system described `in our copending application' `entitled Push-pull modulation system (led of even date herewith) is suitable for use in the system Vof Fig. 9. According to such a modulating arrangement, a clipping circuit similar to thatshown Ain Fig. 8 `has its output phase inverted and applied to a detector of the grid leak typehaving a narrow grid base. Because of the inherent bias adjusting action of the grid leak, the applied cusp'ed wave derived from the clipping circuit of Fig'. 8 is automatically alined so that only the most positive tips of the cusps exceed the grid current threshold, Because of the narrow grid base, only the portions adjacent these tips `lie above thecurrent threshold and are transmitted; ,'.Such an arrangement which skims the cusps may be used to serve the purpose, which in the present invention is served by two diiferentiating circuits following Vtheclipping circuit. In incorporating such a modified pulse producer in the system of Fig. 9,the apparatus 900 would be assumed to includeany desired amount of pre-amplication, thenfa,` clipping circuit according to Fig. 8 followed by a cusp skimming arrangement, as just described.

Although certain embodiments of cui` invention have been shown and described for purposes of illustration, it will be clear that many modifications, additions and omissions may be made thereof, `as defined in the appended claims.

What is claimed is: l i l. A time modulation system 'comprising a source of foundationwaves having a frequency to said circuit for passing `only every Mth one of said produced pulses.

2. A time modulation system comprising a source of foundation waves having a frequency times the desired pulse recurrence frequencywhere M is an odd integer greater than 2, means for producing a pulse in response to each passage of said foundation wave through a predetermined amplitude level, a blocking circuit, means for deriving fromv said source a control wave, means` for applying said vproduced pulses to said blocking circuit, and .means for applying said control zwavezztosaidlcircuit rior-passing only .feveryrMtliLone-zfofb sai'di produced ipulses;

.3. .A'stirne modulation'zsystem comprisingfitransa :mfittingi :meansi-having fafzpair of rectiiiers conmeans kfordetermining Athe=potential`of said input connection relative'to'rthe axis potential of said wave,`second'control-nreans for :determining lthe potential A of "'the; 'circuit' connection between the 'two'rectiers third Icontrol means Afor determining thekload' impedance-at said output connectionaf'sourceof :sig-nal energy, whereby Agate limits are "produced 'by "the l-mutual action of said control` means; and-'meansto apply Vsig-nal 'Yenerg'yjfrom .saidY `source to 'one' of said controlV meansto' infect-variations in `the relative rela- Ytion'of itihiepotential Pof the'axis of said foundatiorrwave and4 at 'least one v4of *said* gate limits.

14;' The .system` defined inN claimS wherein the .means 'for applying signal energy .'to one of said control means' Lincludes means for applying the .signal energy to. said'firs't 'control means, wherebytheaxi'spfsaid "foundation wave is varied according to;tlie signalenergy relative to .given gate limitlpntentials.

5'.'..,'Ihe.sys'tem denedfiri claim 3 wherein the Vmean'sgfor.-,applyirig signal energy to. one of. said control-@means ,includes `.means for. applying the signal.. energy to vsaid..secondl control means,

whereby saidvariationpfsai'd one gate limitincludesA variation of theother-ofJsaidgate limits inv theppposite: direction htov the variation of. said one. gate. limit. Y Y Y 6.Y The/system defined in-c1aim.3 wherein the meanslforcapplying. signalenergy to one of said control means .includes =means for applying the `signals-energy to:said.:third control means, wheresaid gthreshold lunderrcontrol 'of said signal wave, while maintainingsaid i reference axis of said foundation i wave iat-said fixed amplitude where-- by said instants aredisplaced fin time; and means -fortwicedifferentiating said transmitted wave t-o l derive :pulses corresponding to said instants.

8. Asystem according to fclaim "7 wherein said foundation wave is of flxedamplitude and'said `means fonvaryingthe. amplitude level of said 'threshold with' lrespect, to said*Y foundation wave comprises means for Varying the absolute amplitude between said threshold and said fixed refn erence axis of said foundation wave.

t9, `A-fsystem accordingtoclaim 7 wherein said meansfor varying the 4amplitude level of said threshold With-respect tosaid foundation wave .comprises'means for biasing' the threshold by a xe'dgamount with respect toi-said .xed reference axisfof saidfoundationwave and means for Varyingr Athev amplitude: of: said; foundation Waves "whereby .said .,Iixedbiasrrepresents :a relatively yvariable zainplitudrleirel-wvith respect tosaid -xed reference. axisvoffsaidfoundation wave;

10. A` timemodulation s ystem-comprising a source of foundation waves of fixed. frequency having a relatively-,xedf referenceV axis of` amplitude, transmitting means having anfinput con- .nection to which 'a .wavaof Y.said `'source is Yapplied and gate limitsfor limiting the -passage-.,of.energy dependent on rrelativeamplitude levels-of upper andlower-limitsofisaid gate'toasaid xed reference raxis-of said: foundation wave, vfi-rstcontrol means: for 'determining theramplitudefof said input connection `thereby;controlling rsaidfreference axis of amplitude of said wave relative tovgiven amplitude limits I lfor.` Y said @gate v.second control `means for 1- determining-the lamplitude -of the upu per limit of -said gatethirdfcontrol meansffor determining the tamplitudeeof'the llower 'limit of said gate,- favsourcee of -fsignal lenergy, Tmeans y for applying saidfsignaLenergy--to one-of said `-control means to eifect Variations in the relative amplitude between said reference axis of said foundation wave and at least one of said gate limits Whilemaintalning said reference axisatits fixed value,.. whereb'ylrthe output wave of said transmittingmeans has discontinuities corresponding tothe instants` at i which said yfoundation wave is at .the v.same ,amplitude level .as .said one `sate limit, and .doublediiferentiation means for producing .fromsaid output. ,wavepulses displaced .time .accordingto the l.occurrence .of said instants. v

11. A time modulation system! comprising a source of foundation waves of xed frequencyY having a relatively xedreference axis of amplitude, transmitting means having an input connectionto which alwavefromsaid source is ap- Vpliedand gate .limits.forflimitingithe passage of energy dependent upon, the-,relative ramplitude levels fof upper;and'lowenlimits.ofsaid gate with respect to said .referenceaxisof said .foundation wave, means*foredeterminingl the amplitude of said input connection-thereby controlling ksaid reference axis of saldf-wave `relative tol given amplitude limits forfsaidngate,4 control means for determining the amplitude. ofthe .uppers limit of said gate, control meansa fori determining-f the amplitude of -thelower limit-1ofsaid-gate, asource .of signal-energy, means'f-forapplyingsaid signal energy to one of said control means to affect variations in the relative amplitude betweensaid reference axis yof* saidffoundationwaveand at least one off-said .gate-limitsfwhne. maintaining said reference axis-of y:said foundation waveat its relatively fixed valuewith respectftovsaidsignal wave, whereby theoutputsvavelof said-transmitting meanshas discontinuities'corresponding to the instants-atrwhich'said foundationwave isiat the same-:amplitude asfsaidpneagate limit, and meansgfor-producing from :said output wave pulses `displaced in time accordingfto the occurrence'of saidinstants.

12..A-. timev 'modulationz-.system comprising a source1 of: foundation 4=Waves=of -xed vfrequency having a. relativelyxed references axis of'aniplitude, transmittingmeans'1having an iinput :conh nectionnto which -af waveffromxsaid source is `applied andiY gate limitsxrior. :limiting .the passage ofY energyxdepending upontherelative amplitude level of. upper and flowery `limits `.ofisaid gate with 1'espect;to.saidA reference 'axis-lof, said 'foundation wave, meanspfc'irA Adetermining-'the amplitude of said input'connection thereby. controllingthe reftude-.limitss\for saidifgate; Icontrol'Jmeans for determining the amplitude of the upper limit of said gate, control means for determining the amplitude of the lower limit of said gate, a source of signal energy, means for applying said signal energy to the first mentioned control means to effect variations in the relative amplitude between said reference axis of said foundation wave and said upper gate limit while maintaining said reference axis at its relatively fixed value with respect to said signal wave whereby the output wave of said transmitting means has discontinuities corresponding to the instants at which said foundation wave is at the same amplitude as said one gate limit, and means for producing from said output wave pulses displaced in time according to the occurrence of said instants.

13. A time moduatlon system comprising a source of foundation waves of fixed frequency having a relatively iixed reference axis of amplitude, transmitting means having an input connection to which a wave from said source is applied and gate limits for limiting the passage of energy dependent upon the relative amplitude levels of upper and lower limits of said gate with respect to said reference axis of said foundation wave, means for determining the amplitude of said input connection thereby controlling the reference axis of said wave relative to given amplitude limits for said gate, control means for determining the amplitude of the upper limit of said gate, control means for determining the amplitude of the lower limit of Said gate, and a source of signal energy, means for applying said signal energy to the second mentioned control means to affect variations in the relative amplitude between said reference axis of said foundation wave and said lower gate limit while maintaining said reference axis of said foundation wave at its relatively fixed value with respect to said signal wave, whereby the output wave of said transmitting means hasl discontinuities corresponding to the instants at which said foundation wave is at the same amplitude as said one gate limit, and means for producing from the output waves pulses displaced in time according to the current at said instants.

14. A time modulation system comprising a` source of foundation waves with fixed frequency having a relatively xed reference axis of amplitude, transmitting means having a connection to which a wave of said source is applied and gate limits for limiting the passage -of energy depending upon the relative amplitude level of upper and lower limits of said gate with respect to said reference axis of said foundation wave, means for determining said reference axis to said foundation wave, means for determining the amplitude of said input connection thereby controlling said reference axis of said wave relative to given amplitude limits for said gate, control means for determining the displacement between upper and lower limits of said gate, a source of signal energy, means for applying said signal energy to said control means to effect Variations in the absolute amplitude between said gate limits while maintaining said reference axis of said foundation wave at its relatively fixed value with respect to said signal wave, whereby the output wave of said transmitting means has discontinuities corresponding to the instants at which said foundation wave is at the same amplitude as said gate limits and means for producing from said output Wave pulses displaced in time according to the occurrence of said instants.

15. A time modulation system comprising a source of foundation waves having a frequency times the desired pulse recurrence frequencywhere M is an odd integer greater than 2, means for producing a pulse in response to each passage of said foundation wave through a predetermined amplitude level, and means for passing only every Mth one of said produced pulses, said means for producing a pulse in response to each passage of said foundation wave through a predetermined amplitude level comprising non-linear transmitting means having a discontinuity threshold and connected to transmit all portions of said waves which lie on a given side of said threshold, whereby the transmitted waves have corners corresponding to the instants of intersection of said foundation waves with said threshold, a source of signal waves, means for varying the position of said threshold with respect to said foundation waves under control of said signal waves, whereby said instants of intersection are displaced in time, and means for doubly differentiating said transmitted waves to derive pulses corresponding to said corners.

16. A method for decreasing the time displace'- ment for a signal modulated pulse on a time modulated pulse wave comprising generating a foundation wave having a frequency greater than that of the desired pulse recurrence frequency, deriving pulses from said wave, modulating said pulses with said signal to produce time modulated pulses at said greater frequency, and eliminating sufficient of said pulses to obtain a time modulated pulse wave having said-desired pulse recurrence frequency.

EMILE LABlN. DONALD D, GRIEG.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,315,529 Carson Sept. 9, 1919 2,086,918 Luck July 13, 1937 2,113,214 Luck Apr. 5, 1938 2,061,734 Kell NOV. 24, 1936 1,655,543 Heising Jan. 10, 1928 2,280,707 Kell Apr. 2l, 1942 2,227,596 Luck Jan. 7, 1941 2,324,275 Becker July 13, 1943 2,188,611 Norton Jan. 30, 1940 2,208,422 I-Iugon July 16, 1940 2,209,395 Fitch Julyl 30, 1940 2,022,969 Meacham Dec. 3, 1935 2,113,011 White Apr. 5, 1938 2,221,666 Wilson Nov. 12, 1940 

